1. Field of the Invention
This invention relates to a scanning system where a movable body with a light source for projecting reading light is linearly moved to cause the reading light to scan the radiation image recording medium.
2. Description of the Related Art
There have been proposed and put into practice, for instance, in the medical field various radiation image recording media which are irradiated by radiation passing through an object and stores therein a radiation image of the object.
As such a radiation image recording medium, there has been known, for instance, a radiation image sensor using semiconductor material which generates electric charges upon projection of radiation and a stimulable phosphor sheet using stimulable phosphors which store radiation energy upon projection of radiation and emit evanescent light upon projection of reading light.
When a radiation image is read out from such a radiation image recording medium as an electric signal, a reading light source emitting a line-like reading light beam is employed and is moved in a direction substantially perpendicular to the longitudinal direction thereof to cause the line-like reading light beam to scan the radiation image recording medium in view of increasing the reading speed. (See U.S. Pat. No. 6,268,614.)
Recently, from the viewpoint of reduction of the overall size of the system, a system where both the radiation image recording medium and the scanning system for causing the reading light beam to scan the radiation image recording medium are accommodated in one cassette. By the use of such a cassette, after a radiation image is recorded in a radiation image recording apparatus, the radiation image can be immediately read, and it is possible to correct the radiation image taking conditions viewing the read out radiation image.
In the radiation image recording apparatus, the reading light source must be moved sometimes for scanning in a direction inclined to the horizontal when the cassette is inclined in various directions according to the image taking conditions as in mammography.
The scanning system built in the cassette causes the mobile body (or the reading light source) to wait in a predetermined waiting position for a time other than when the reading light beam is to scan the radiation image recording medium. When the mobile body must be moved in a direction including the vertical components, it is necessary to hold the mobile body in the waiting position by a drive means such as a linear motor. Accordingly, there has been a problem that the drive means consumes power even if the mobile body is waiting. The power consumption of the drive means is increased as the direction in which the mobile body is moved approaches the vertical.
Further, it is not preferred from the viewpoint of generation of heat to drive the drive means, such as the linear motor, for a long time.